Stabilizer for pressure fluid servomotors



Dec. 2, 1947. A. G. LARSON STABILIZER FOR PRESSURE FLUID SERVOMOTORS 2 Sheet-Sheet 1 Filed March 30, 1944 IN VEN TOR ATTORNEY Am F: I 3 r mq 5.

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A. G. LARSON 2,431,759

STABILIZER FOR PRESSURE FLUID SERVOMOTORS Filed March 30, 1944 2 Sheets-Sheet 2 IN VEN TOR A TTORNE Y Arthur G. Larson- Patented Dec. 2, 1947 UNITED STATES PATENT OFFICE STABILIZER FOR PRESSURE FLUID SERVOMOTORS Application March 30, 1944, Serial No. 528,691

3 Claims. -1

This invention relates to stabilizers for control apparatus and more particularly to means for preventing unwanted movement of an operating or operated member.

In my copending application Serial No. 470,803, filed December 31, 1942, and issued as Patent No. 2,418,129 on April 1, 1947, there is disclosed a fluid motor of the so-called follow-up type embodying a power piston and a regulating valve device for establishing differentials in fluid pressures on said piston for moving same, and for destroying said differentials to stop movement of the piston. Pilot means in the form of a piston is arranged to actuate the regulating valve device to create the differentials in fluid pressures on the power piston, while the power piston is arranged to actuate the regulating device to destroy the differentials in fluid pressures upon the power piston attaining a position corresponding to operation of the pilot means.

In fluid motors of this general type it is desirable that the power piston promptly move to and stop in a position determined by operation of the pilot means. However, in case the resistance to movement of the device operated by the power pis ton is variable, such for instance as to require a greater differential in pressures on the piston to move it during a portion of its stroke than may exist near the position in which it is desired that the power piston will stop, the differential in pressures acting on the piston, aided by inertia of said piston and possibly of the parts being operated, will tend to cause the power piston to over travel and consequently move the device being operated past the position in which it is desired that it be stopped. If the power piston should thus overtravel it will operate the regulating device to reverse the differential in fluid pressures on the power piston and thus cause said piston to reverse its direction of movement. This reversal of the power piston may then result in over-travel in the opposite direction, and consequently another reversal in the direction of movement of the power piston may result. Such oscillation of the power piston is undesirable particularly where it is desired to position a device with a relatively high degree of accuracy.

One object of the invention is therefore the provision of means arranged to obviate the above difficulty.

Another object of the invention is the provision of a stabilizer for a reciprocatory piston or the like so constructed and arranged as to allow relatively free movement of the piston from one position substantially to another or selected position, and

which is effective upon the piston attaining theselected position to stop said piston and substantially lock same against movement out of the selected position.

I attain these objects b the use of a novel hydraulic dash-pot or stabilizer the piston means of which is connected to move with the power piston. The stabilizer piston means is opposedly subject to liquid in two chambers which are in constant communication through a small port, and a by-pass valve is provided to open and close a relatively large communication between said hambers. This by-pass valve is connected for movement with the pilot means and is so designed as to open the communication controlled thereby upon movement of the pilot means to effect operation of the regulating valve device to establish a differential in fluid pressures on the power piston, whereby the stabilizer piston means may move relatively freely with the power piston as the latter moves toward a selected position. Upon cessation of movement of the pilot means, the continuing movement of the power piston will then actuate the by-pass valve to close the communication controlled thereby; the by-pass valve effecting closure of said communication just before the power piston attains the selected position.

It will be apparent that if closure of the communication controlled by the by-pass valve completely bottled the liquid efiective on the stabilizer piston means, the power piston would stop suddenly and impose severe shock, not only on itself, but also on associated mechanism. I avoid such shock however by use of the port constantly connecting the two chambers, whereby upon closure of the by-pass valve the relatively small flow of liquid still possible from one of the chambers to the other will arrest movement of the power piston without undue shock. Further movement of the power piston to its selected position will then be so retarded as to insure operation of the regulating valve device to substantially equalize the opposing fluid pressures on the power piston by the time the power piston attains its selected position. The differential in pressures thus being destroyed on the power piston when it attains the selected position and further movement being opposited by the dash-pot or stabilizer, said power piston will stop moving and the stabilizer will then hold it against unwanted movement out of the selected position.

Other objects and advantages will be apparent from the following more detailed description of the invention.

In the accompanying drawings; Fig. 1 is a side view, partly in section, of a fluid motor of the follow-up type and of the stabilizer embodying the invention; Figs. 2 and 3 are sectional views taken substantially on the lines 2--2 and 33 in Fig. 1; Figs. 4 to 7 are sectional views taken on the lines 4i, 5-5, 6-5, and 1-1, respectively. in Fig. 3; Fig. 8 is a sectional View takensubstantially on the line 88 in Fig.1; and Fig. 9 is a sectional view of a pressure regulating valve device associated with the motor shown in Fig. l and taken in a plane parallel to but back of the plane of the section in Fig. 1.

Description In the drawings, the reference numeral I indicates a fluid motor which for the purpose of illustrating one use of the invention, may be substantially like that disclosed in the aforementioned pending application, in view of which the following description of the motor will be limited to only those details necessary to a full and complete understanding of the invention.

The fluid motor I is secured to a mounting plate 2 and comprises a cylinder containing a power piston 4 having at one side a pressure chamber 3. The piston i has a rod 5 projecting therefrom through a pressure chamber 6 at the opposite side and a suitable opening in .a pressure head 3 closing the open end of said chamber. The outer end of the rod 5 is connected by a pin ,8 to one end of a link 9. The other end of link 9 is connected by a pin II! to a gear sector II at a point remote from a pin I2 secured to the mounting plateZ. The pin I2 constitutes a fixed fulcrum upon which the gear sector I I is mounted to turn.

The teeth of the gear sector II have driving engagement with teeth on a gear I3 which is connected to a sprocket wheel I4. Gear I3 and sprocket wheel I 4 are mounted for rotation in unison on a pin I5 carried by the mounting plate 2. The sprocket wheel I4 may be connected by a chain (not shown) to a device which it is desired to operate or move to different selected positions. It will be apparent that movement of piston 4 in one direction in its cylinder will turn the sprocket wheel I4 in one direction, while movement of said piston in the opposite direction in said cylinder 3 will turn said sprocket wheel in the opposite direction. By selecting the direction and limiting the extent of movement of the power piston 4 selective positioning of the sprocket wheel Hi and of the device operated thereby may therefore be obtained.

Associated with the pressure head I is a fluid pressure regulating valve device I6 comprising pressure control valve devices I1 and III for controlling the supply andreleaseof fluid under pressure to and from the respective chambers 6 and 3 at opposite sides of the power piston 4.

Both of the pressure regulating valve devices I! and I8 may be identical in construction, each comprising, as shown in Fig. 9, a fluid pressure supply valve I30 contained in a chamber I3I and having a fluted stem I32 extending through a bore in the casing into a chamber I33, said valve being provided to control the flow of fluid under pressure from chamber I3I to chamber I33. A spring I34 acts on each supply valve I30 for urg ing it toward its closed position.

Each of the regulating valve devices I! and I8 further comprises a fluid pressure release valve I35 formed on a member I36 which bears against the end of the respective fluid pressure supply valve stem I32. Each release. valve I35 has a fluted stem mounted to slide in a bore I37 provided in a plunger or sleeve I9 which is slidably mounted in the casing. In chamber I33 each plunger has a seat for engagement by the respective release valve which is thus arranged to control communication between said chamber and bore I31. Each plunger I9 extends beyond the exterior of the casing and is provided with one or more radial bores I39 connecting the respective bore I37 to atmosphere. Further each plunger I9 is provided in the release valve chamber I 33. with a collar Hi9 encircling the release valve seat, while a similar collar MI is provided on the end of member I36 eng ging the supply valve stem I32, and interposed between and bearing against these collars in each valve device is a precompressed spring M3 acting to urge the plunger I9 in a direction out of seating engagement with the release valve I35. The casing is provided with an annular groove encircling and open to the peripheral surface of each plunger I9 and in this groove is disposed a resilient ring IM providing sealing contact between the casing and said plunger for preventing leakage of fluid under pressure from the release valve chamber I33 past said plunger to atmosphere.

The supply valve chamber I3I is common to both regulating valve devices I I and I8 and is adapted to be constantly supplied with fluid under pressure from any suitable source by way of a pipe Hi5 and a passage I46. The release valve chamber I 33 in the regulating valve device I? is in constant communication with the power piston chamber 6 through a passage Ml, while the corresponding chamber in the regulating valve device I8 is in constant communication with the power piston chamber 3 through a passage I48 passing back of the release valve chamber i3? in the regulating valve device I! and connected to a passage I49 which extends through the power cylinder and opens to chamber 3 at the outer end thereof.

In each of the regulating valve devices I? and. I8, the supply valve I33, release valve I35 and plunger I9 are arranged in coaxial relation, and these parts in the two valve devices are spaced apart and arranged in parallel relation.

A shaft 29 arranged midway between the two plungers I9 is journaled adjacent its opposite ends in spaced brackets 2! extending from the pressure head 1. Between the brackets 2! a sleeve-like member 22 mounted on shaft 20, and as best shown in Fig. 2, is secured by a pin 23 to turn with said shaft. The member 22 ha two oppositely extending arms 24, one disposed over each of the plungers I9. In the end of each arm 24 is secured an adjusting screw 25 for engaging the respective plunger I9. For operation of the structure the two adjusting screws 25 are adjusted in the manner which will now be described.

With the supply valve chamber H34 in the two regulating valve devices I7 and i8 supp-lied with fluid under pressure from pipe M5 through pas sage Hi5, and with the two arms 2d of member 22 extending parallel to the axis of the power piston rod 5, the two screws 25 are turned into cngage- I ment with the ends of the respective plungers I9 the power piston 4, and at the same time through passages I48 and I49 to chamber 3 at the opposite side of the power piston 4.

The adjustment of both screws 25 may be such as to unseat the supply valves I30 to such an extent as to allow pressure of fluid supplied to the supply valve chambers I 3| to equalize into chambers 3 and 6 at opposite sides of the power piston, or in other words, the adjustment may be such as to maintain the supply valves open. However it is preferred that both of the supply valves I30 be unseated to a lesser degree such that when a certain pressure, intermediate that of the atmosphere and that supplied through pipe I45, is otbained on the opposite sides of the power piston, such pressure acting in chambers I33 on the ends of the respective plungers I9 will urge said plungers outwardly sufliciently to allow the two supply valves I30 to seat. With this latter adjustment the supply valves I30 will initially be unseated by screws 25 a very small degree, such for example as one one-thousandths of an inch, under which condition is has been found that both of the supply valves I30 will seat upon obtaining the desired intermediate degree of pressure on opposite sides of the power piston 4.

Whether the adjusting screws 25 are adjusted to hold the supply valves I30 open to permit full supply pressure to be obtained from pipe 5:25 on opposite sides of the power piston or whether they are adjusted to allow closure of the supply valves upon obtaining the intermediate degree of pressure on opposite sides of the power piston, it will be apparent that substantially the same pressure of fluid will be effective in both pressure chambers 3 and 6 on opposite sides of the power piston 4.

The area of piston 4 subject to pressure of fluid in chamber 6 is less than the area subject to pres sure of fluid in chamber 3 by an amount equal to the area of the piston rod 5, and it will therefore be seen that when the pressures of fluid acting on opposite sides of said piston are the same, there will be a slight differential in the opposing forces created on said piston which will tend to move said piston toward the left hand. This differential in forces is less however than the static resistance to movement of the piston and of other parts of the structure which said piston is adapted to move. It will therefore be seen that when the pressures of fluid in chambers 3 and 6 are substantially the same, the piston 4 will be in a static or stationary condition.

With the parts conditioned as just described, it will be noted that a slight degree of rocking of member 22 in a clockwise direction, as viewed in Figs. 1 and 9, will permit operation of the valve device I8 to release fluid under pressure from the power piston chamber 3 and at the same time will actuate the valve device I! to increase the pressure of fluid in chamber 6, in case it is not already equal to that in the supply pipe I35, for thereby creating a differential in pressures of fluid on the power piston which is efiective to move said piston in the direction, of the right hand. Rocking of member 22 in a counter-clock wise direction wil create an oppositely effective diiferential in fluid pressures on the power piston to move it toward the left hand. Return of member 22 to its normal position will destroy a diiierential in fluid pressures on the power piston to cause cessation of movement of said piston, as will be apparent. It will thus be seen that by suitable manipulation of member 22, the power piston 4 can be caused to turn the sprocket wheel I4 in either direction and stop it in desired position at either side of and including its normal position, in which it is shown in the drawing,

Associated with the end of the power cylinder 3 opposite the pressure head I is a pilot device 33 for controlling operation of the member 22 to provide differentials in fluid pressures on the power piston 4. The pilot device 39 comprises a casing structure secured to the power cylinder and containing two oppositely and axially arranged fieX- ible diaphragms 3| and 32 having at their respective outer faces pressure chambers 33 and 34 connected to control pipes 35 and 33, respectively. The pipes 35 and 36 may lead to any suitable con trol valve device (not shown) which is operable to supply fluid at any selected pressure, from zero {pressure to a maximum degree to either one of said pipes while maintaining the other pipe open to atmosphere.

The two diaphragms 3i and 32 are connected together for movement in unison by means including a rod 3'! and followers 38 and 33 respectively engaging the adjacent faces of said diaphragms. The follower 38 is arranged to engage a shoulder 40 in the casing to limit deflection of the diaphragms in one direction, while a similar shoulder 4| is provided for engagement by follower 33 to limit deflection of the diaphragms in the opposite direction.

Intermediate the two diaphragms 3| and 32, the rod 37 is operatively connected by a pin 42 to a lever 43 one end of which is mounted to turn on a pin 44 secured in the casing structure. The opposite end of lever 43 is connected to one end of a rod 45 projecting from a resistance device 43 secured to the power Cylinder 3. The resistance device 46 may contain spring means (not shown) arranged to oppose with increasing pressure, movement of lever 43 in either direction from a neutral position in which it is shown in the drawing, and said spring means is therefore constantly effective to bias said lever toward its neutral position.

It will now be seen that upon supply of fluid through pipe 35 to diaphragm chamber 33 with diaphragm chamber 34 open to atmosphere through pipe 36, the diaphragm 3| will deflect and rock lever 43 in a clockwise direction to a position in which the pressure of resistance means 45 balances the pressure of such fluid. Any selected position of lever 43 at the right-hand side of neutral position may therefore be obtained by the provision of fluid at a suitable pressure in chamber 33. of lever 43 will be obtained by providing fluid in chamber 33 at a pressure sufllcient to move the follower 38 into contact with shoulder 43. In a like manner the lever 43 may be moved to any selected position at the left-hand side of its neutral position by providing fluid at a suitable pressure in diaphragm chamber 34. Release of fluid pressure from either chamber 33 or 34, with the other chamber vented, will render the resistance means 46 effective to position the lever 43 in accordance with the reduction in such pressure, while a complete reduction in such pressure to that of the atmosphere will render the resistance device eifective to move lever 43 to its neutral position, as will be apparent.

The member 22 disposed between the fluid pressure regulating devices I? and I8 has an upwardly extending arm 59 in the end of which is a pin 5|. An equalizing lever 52 is fulcrumed intermediate its ends on the pin 5i. One end of the equalizing lever 52 is pivotally connected The extreme right-hand position to one end of an operating rod 53 which extends through space provided between the resistance device it and the power cylinder 3 and which has its opposite end pivotally connected by a pin 55 to lever 33 adjacent its'connection with rod d projecting from the resistance device 35. The opposite end of the equalizing lever 52 is pivotally connected to one end of a rod 55 the opposite end of which is connected to a pin 56 secured in an arm 5'! projecting from the gear sector H at the side of the sector fulcrum pin [2 opposite the connection between said sector and piston rod link 9.

The operation of the fluid motor above described is briefiy as follows:

Let it be assumed that the various parts of the structure are in the positions shown in Fig. 1 and that is desired to turn the sprocket wheel it in a clockwise direction from the neutral position shown in the drawing to a different selected position, which requires movement of power piston t in the direction of the right-hand. To accomplish this, fluid at a selected pressure is supplied through pipe 35 to diaphragm chamber 33 which causes deflection of diaphragm 3i and thereby rocking of lever 43 in a clockwise direction to a position corresponding to the pressure of such fluid, assuming such pressure to be less than required to deflect said diaphragm its full travel.

This movement of lever 43 actuates rod 53 to turn lever 52 in a counterclockwise direction about its fulcrum connection with rod 55 which at this time will be held stationary due to the relatively great reluctance to movement of the connected power piston 4. This rocking of lever 52 about its fulcrumed connection with rod 55 therefore rocks lever 50 and member 22 in a clockwise direction which actuates the fluid pressure regulating devices I! and E8 to create a differential in the pressures of fluid in chambers 3 and 6 which is effective to move said piston in the direction of the right hand, and this movement in turn turns the sprocket wheel M out of its neutral position in the direction of the position which it is desired it shall attain.

The power piston A may start moving as just described before the diaphragm 3i attains its pressure determined position above mentioned, but after deflection of said diaphragm ceases, the rod 53 and the connected end of equalizing lever become stationary. Continued movement of the power piston 5 relative to diaphragm 3! then acts through the medium of the gear sector H and rod 55 to rock the equalizing lever 52 in a counterclockwise direction about its connection with rod 53 and this moves the lever 50 and member 22 back toward their neutral positions. When the neutral position of member 22 is attained the valve devices I? and I8 will have operated to destroy the differential in fluid pressures on the power piston to cause it to cease moving for thereby stopping sprocket wheel [4 in the position corresponding to the pressure of fluid provided in diaphragm chamber 33.

If it is desired to turn the sprocket wheel [4 furtherin the same direction to another selected position, the pressure of fluid is increased in chamber 33 to a still higher degree, and the apparatus will again operate as just described to turn said wheel to the new selected position.

On the other hand, if it is desired to turn the sprocket wheel back toward, but to a selected position still out of neutral position, the pressure offluidin diaphragm chamber 33 may bereduced to the degree corresponding to the new desired position of the sprocket wheel. This reduction in pressure of fluid in chamber 33 permits resistance device 46 to rock lever 43 in a counterclockwise direction and deflect diaphragm iii to a position corresponding to the reduced pressure of fluid, and this movement of lever 43 transmitted through rod 53 and equalizing lever 52 turns the lever Ell and member 22' in a counterclockwise direction which actuates the valve devices l1 and [8 to create a differential in fluid pressures on the power piston 4 which acts to move said piston toward the left-hand. After the diaphragm 3| obtains the position corresponding to the reduced pressure of fluid in chamber 33, the movement of the power piston then rocks lever 59 and member 22 in a clockwise direction back toward their neutral position. When the neutral position of member 22 is attained, the valve devices I! and I8 will again have operated to destroy the differential in fluid pressures on the power piston 4 and said piston will cease movement in a position, it will be noted, corresponding to the position of control lever 33 and thus in accordance with the reduced pressure of fluid in diaphragm chamber 33.

A further reduction in the pressure of fluid in chamber 33 will cause the sprocket wheel 14 to assume a corresponding new position back toward its neutral position, while a complete release of fluid under pressure from said chamber will cause said sprocket wheel to be returned to its neutral position, as will be apparent from the above description.

It will now be seen that the sprocket wheel l4 may be caused to assume any desired position at the right-hand side of its neutral position by the provision of fluid at the proper selected pressure in diaphragm chamber 33. The sprocket wheel it may also be caused to assume any desired position at the left-hand side of its neutral position by providing fluid at the proper selected pressure in diaphragm chamber 34, in a manner which will be apparent from the above description and which therefore need not be described in greater detail.

For reasons before set forth there is, however, a possibility that piston 4 may not stop in a selected position as above described, but may overtravel the selected position, in which case its direction of movement may be reversed and resuit in over-travel of said position in the opposite direction. Such over-travel of the power piston would be undesirable and, in accordance with the invention, may be prevented by a dash-pot or stabilizer which will now be described.

In the drawing the stabilizer is indicated generally by the reference numeral 69 and, as shown, comprises a casing 61 secured by bolts or screws 62 to the mounting plate 2 in the space between the follow-up rod and piston rod 5 and between the gear sector i and equalizing lever 52.

The casing El has two coaxially aligned oppositely extending open-ended bores $3 and 84 separated by a dividing wall and arranged in substantial parallel relation to the piston rod 5, as viewed in Fig. 1 of the drawing. A piston is disposed in bore 63 and an oppositely arranged piston 6? is disposed in bore 84, the two pistons being connected together for movement in unison by a rod 68 extending through a bore in the dividing wall 65 and having a sliding fit with the wall of said bore. The two pistons 66 and 61 have at their adjacent faces pressure chambers 69 and Iii respectively, which are constantly filled with a suitable liquid such as oil whereby the two pistons are constantly opposingly subject to the liquid in said chambers. The two chambers 69 and 19 are constantly in communication with each other through a relatively small port or choke 85 provided through the dividing wall 65. The opposite faces of the two pistons are subject to atmospheric pressure through the open ends of the respective bores.

The piston 66 comprises a piston head II having substantial sliding contact with the wall of bore 03 and having an annular groove in which is disposed a resilient ring 12 having sealing and sliding contact with the wall of said bore. v

Mounted against the face of piston head iI adjacent the pressure chamber 69 is the central annular portion of a flexible packing cup I3, the peripheral substantially cylindrical portion of which extends into pressure chamber 69 and has sliding sealing contact with the wall of said chamber. A follower M is secured against the opposite face of the packing cup 13 by a nut 15 on the piston rod 68. l

The piston 61 comprises two rings I6 and H which are slidably mounted on a reduced portion of piston rod 68 disposed in bore 64. The ring I6, constituting a follower, is in contact with a shoulder F8 on the piston rod, and clamped between the two rings by a nut i9 having screw-threaded engagement with the rod and engaging the outer face of ring TI is the central annular portion of a flexible packing cup 80. The packing cup 89 is like the packing cup 13 but oppositely arranged, that is, it has its peripheral sealing portion extending into chamber I0. The ring 11 constitutes a piston head and carries a resilient ring 9| having sealing sliding contact with the wall of bore 64.

The piston 66 carries a pin 82 connecting said piston to one end of link 83. The opposite end of link 83 is connected by a pin 84 to gear sector I! between the fulcrum pin I2 and the connection with the power piston rod connecting link 9. The two pistons 66 and 61 are therefore arranged to move with the gear sector II and power piston i.

The casing of the stabilizer has a raised part 86 extending upwardly from the dividing wall 65 into an oil reservoir or sump 8'! which extends substantially the length of the structure over the piston bores 63 and 64. The length of the raised part 95 is less than the width of the oil reservoir so that said reservoir extends down past the opposite ends of the raised part, as shown in Fig. 8 of the drawing. One or more openings closed by screw-threaded plugs 88 are provided for filling the reservoir 81 with oil.

The raised portion 86 in the casing has a through bore arranged at right angles to the stabilizer piston rod 68 and into this bore is pressed a bushing 90. A plug valve 9I is mounted to rotate in bushing 90. The end of this valve adjacent the mounting plate 2 contacts the inner face of a plug 92 secured in and closing an opening in the casing. The opposite end of the valve 9! bears against the inner face of a plug 93 secured in and closing another opening in the casing. The valve 9| is provided with an operating shaft 94 which extends through a central bore in the plug 93 to the exterior of the casing, and on the outer end of th s shaft is secured one end of an operating arm 95. The opposite end of arm 95 is connected to one end of an operating rod 96 the opposite end of which rod is connected to an arm 91 secured by a pin 98 to the end of shaft 20 projecting beyond one of the brackets 2I. This structure provides for rotating the plug valve 9I in bushing 20 upon the rocking of member 22 by lever arm 50. Within the nut 93 is an annular groove encircling the shaft 94 and containing a resilient ring 99 providing a seal between said shaft and nut to prevent leakage of oil from the reservoir 87.

The raised portion 86 of the casing is provided with four spaced annular grooves 39, IOI, I02 and H33 encircling and open to the outer surface of the bushing 90. The central grooves I00 and iii! are disposed one on either side of the longitudinal center of the bushing, while the grooves I92 and I93 are located one adjacent each of the opposite ends of said bushing. The groove I02 is open through one or more bores I05 to pressure chamber 69, and groove I00 is also open to said chamber through one or more bores I05. The grooves IOI and I03 are open to pressure chamber I0 through one or more bores I01 and I08, respectively.

The bushing has two diametrically opposite ports I09 connecting its interior to the groove 509, and two other aligned ports H0 connecting its interior to groove I02. Diametrically opposite pairs of ports III and H2, arranged 90 from ports 199 and H0, connect the interior of the bushing 92 to grooves IOI and I03, respectively.

In the portion of valve 9| extending over the two middle grooves I00 and II]! and over ports I09 and I I I, are four cavities II5, equally spaced from each other around the valve and connected together by cross ports I I6. These cavities extend longitudinally of the valve and are of such a length as to connect ports I09 and III under conditions to be later described, but their width is such that between each two adjacent cavities there is a peripheral portion II! of the valve in contact with the wall of the bushing, which peripheral portion is slightly wider than ports I00 or III.

With the valve 9| in the neutral position shown in Figs. 5 and 6 of the drawings, two opposite peripheral portions III cover ports I09, while the other peripheral portions II'I cover the ports III, thereby closing communication between the ports I09 and Ill and thus between the two pressure chambers 69 and 10. The turning of valve 9| in either direction from neutral position to a slight degree will open communication between ports I09 and two oppositely arranged cavities I I5, and will also open ports I I I to the other two cavities H5, and since all of the cavities II5 are connected together by the cross ports H6, the opening of this communication will allow flow of liquid from one of the pressure chambers 69 or I0 to the other depending upon the direction of movement of the stabilizer pistons 66 and 6'!. The flow capacity of this communication will vary according to the extent of movement of the valve 9! out of neutral position in either direction, which governs the degree of opening between ports I99 and II I and cavities H5, and will be gradually reduced as the valve is turned toward neutral position and completely closed just ahead of attaining said position. All of the ports I09 and H0, III and H2 are relatively long, in the direction of the length of the bushing 90, as compared to their width, so as to provide a relatively large degree of opening of the communication above described for a slight movement of the valve out of neutral position and to also maintain a relatively large degree of opening and thus a relatively low resistance to flow of liquid between l l the two pressure chambers, until the valve is returned substantially to its neutral position.

In operation, when fluid under pressure is supplied to deflect either diaphragm 3| or 32, the rocking of lever 43 equalizing lever 52 and lever Eilwill also rock lever 91 and through rod 96 the operating arm 65to turn the valve 9| out of neutral position in either one direction or in the opposite direction. This turning of valve 9| opens communication between pressure chambers 69 and 16 by way of ports I69 and Ill, cavities H5 and cross ports H6 in the valve, so that upon subsequent movementof the power piston 4 and thereby of the stabilizer pistons 66 and 61, liquid displaced by one;or the other of said pistons, depending upon the direction of their movement with therpower piston 41, may with a relatively great degree of freedom flow out of the respective pressure chamber 69 or 16 and into the other pressure chamber, so that the stabilizer pistons will not exert any undue force opposing movement of the power piston 4.

As the power piston 4 then continues to move toward its selected position, it acts, through equalizing lever 52 and levers .56 and 97, to turn the plug 9i back toward its neutral position, and the plug valve will attain its neutral position at the time the power piston attains the position in which it is intended to stop. Due to the shape of ports I69 and III in the bushing, relatively free flow of liquid from the one pressure chamber to the other will however contine until just before th valve attains its neutral position in which further flow of liquid will be prevented.

It will thus be seen that si ce the valve 9! allows relatively free fiow of liquid from one pressure chamber 69 or 16 to the other until said valve is substantially turned to its neutral position, the power piston A will be ab e to move promptly and without undue resistance from the stabilizer substantially to its new or selected position. After the valve 9| is closed the liquid will however continue to flow from one pressure chamber to the other-through the choke 85. The flow capacity of this ch ke is, how ver. uch as to offer relatively great resistance to the flow of oil from-one pressure chamber to the other, so that as soon as the valve 9| is returned to substantially its neutral position, a relatively high oil pressure will develop on th stabilizer piston 66 or 6'! which is displacing oil, to promptly snub the power or piston l, or, in other words, to oppose the actuating force on the power piston and decelerate the rate of movement thereof and thus absorb substantially all of its inertia and that of the connected parts. After the power piston is thus brought to-a substantial stop continued movement will occur only at a rate determined by choke 85 and which will be sufficiently slow to allow operation of the valve device or devices I! or 18 to destroy the differential in pressures on the power piston by the time said piston moves intothe position in which it is intended to stop, so that accurate positioning of said piston'will occur, without over-travel or possible oscillation.

It will be apparent that without the use of choke 85 the closing of the communication between chambers 69 and by the valve 9| would completely bottle up the liquid in both of said chambers which would causesudden stopping of the stabilizer pistons and of the power piston 4 and this could result in damageto or breakage of the structure. The choke 85, however, avoids :the development of damaging shocks, but at the same time creates a force for opposing movement 12 of the powerpiston which.reduces;the rate of movement of .saidpistontoa sufficiently low degreetoobtain accurate stopping thereof in the desired position.

It will beapparentithat the stabilizer will operate inthemanner justdescribedupon each operation of the pilot device 30 and regardless of the direction or extent ofdesiredmovement of the power piston 4.

Adjacent the plug-92 the valve 9| is provided with'two diametrically opposite cavities I 20 for registration with ports H0, and each cavity is connected by a groove. I'2l extending out past the end of the bushing to the oil reservoir Bl, whereby oil from said reservoir will be-constantly presentin said cavities. Similar cavities I22 are provided in the valve adjacent the opposite end of the bushing for registration with ports H2, and each of these cavities is also connected to the oil reservoirBl through a groove I23 provided in the valve and extending out past the end of the bushing.

The valve 9| is so disposed in bushing that with the operating arm in its neutral position as shown in Fig. l the ports H0 and H2 in said bushing will be closed'by said valve. Rotation of the valve 9| ina counterclockwise direction, as viewed in Fig. 1 or in Figs. 4 to 7, as will occur upon movement of the diaphragm operated lever 43 in the direction of the right-hand to efiect movement of the power piston in the same direction, will maintain the ports H6 closed by said valve, but at the opposite end of the valve the cavities I22 will be moved into registry with the diametrically opposite ports I I2 in the bushing so as to thereby open the oil reservoir 8'! to the pressure chamber 10 into which oil is displaced by the stabilizer piston 66 during such operation. Thus during movement of the power piston 4 toward the right hand, the pressure chamber 10 will not only receive the oil displaced by piston66 from chamber 69, but will also be capable of receiving oil from the oil reservoir 81 as the piston 61 is moved away from the dividing wall '65. The purpose of this is to insure that chamber 10 will be maintained completely filled with oil during movement of the piston G! away from thedividing walls 65 so as to prevent a partial vacuumbeing created in said chamber which would tend to allow air from the atmosphere to creep past the packing cup 86 into said chamber. The packing ring'Bl is also provided as a further safe-guard against the entrance of air from the atmosphere to chamber 16 under this condition.

Now in case the valve 91 is turned in a clockwise direction from neutral position, as would occur upon operation of the structure to effect movement of the power piston 4 in the direction of the left-hand, said valve will maintain the ports H2 in the bushing closed, while the ports III] will be opened to cavities in the valve and thus to the oil reservoir, so that as the stabilizer piston 6'! acts to displace oil from pressure chamber iii to chamber 69, oil will also be capable of flowing from the oil reservoir to the latter chamber in order to maintainit completely filled with oil and thus minimize thepossibility of air entering said chamber past the piston 66. The sealing ring [2 is provided .onpiston 66 as an added safe-guard against the entrance of airto chamber 69.

It will be noted that all oildisplaced by either of the stabilizer pistons 66 -or 67, depending upon the direction of their movement, is forced into the space created by movement of the other piston 13 away from the dividing wall 65 and this amount of oil should theoretically fill said space, but in case it fails to do so, the creation of a partial vacuum in said space is prevented by opening said space to the oil reservoir which, in addition to the sealing ring Si or It, ensures that air will not enter either pressure chamber 69 or iii.

In fluid motors of the type above described there is always a possibility of leakage of fluid under pressure from the different pipes and chambers such as chambers 3 and 6 at opposite sides of the power piston. 4. If for instance there should be leakage of fluid under pressure from chamber 5 with the adjusting screws 25 adjusted to permit closure of the supply valves IS!) with the arms 24 in their neutral positions, such leakage would cause a differential to develop between the pressures of fluid in chambers 8 and 3, and when this differential becomes sufficient the piston would start moving toward the left hand. This move ment would then actuate the valve device I? to supply fluid under pressure to chamber 6 and at the same time would allow operation of the valve device I8 to release fluid under pressure from chamber 3 which would not only destroy the operating differential but would also create an oppositely acting differential to move the power piston back to the selected position in which the opposing pressures would again be equalized. Continued leakage would then cause the piston to again move toward the left hand slightly and then back to the selected position. In case the leakage were from chamber 3,. the power piston would tend to move from the selected position toward the right hand and then back to its selected position.

This possible oscillatory movement of the power piston due to leakage is relatively small. For example with a leverage multiplication of ten between the supply valves I30 and power piston. and with the supply valves I39 adjusted to limit the pressure in pressure chambers 25 and 6 to an intermediate degree, approximately one thousandth inch movement of the screws 25 in either direction from their neutral position is adequate to control operation of the fluid pressure regulating devices II and I8 to limit the extent of oscillatory movement of the power piston to approximatel three-sixteenths of an inc-h. It is however desirable that this oscillation of the power piston be opposed by high resistance to insure against over-travel as might tend to occur in case the device being controlled were to exert a force biasing the power piston out of a selected condition. In order to provide this high resistance, I maintain the liquid flow communication controlled by valve QI closed during oscillation of the power piston incident to leakage of fluid under pressure, as just described, such closure being obtained preferably by making the peripheral portions III of the valve 91 wider than the ports I99 and III. Ihus while the power piston may move in case of leakage of fluid under pressure sufiiciently to actuate the valve devices I! and I8 to cause said piston to move back to its selected position, the valve SI will maintain closed its liquid flow communication between chambers 69 and Ill and thus so dampen movement of the power piston that it will not move further than actually required for operating the valve devices I! and I8 to stop said piston and cause it to return to its selected position.

The difference in width between the peripheral portions I II of the valve SI and the ports I09 and III required to accomplish the result just described is however so small as not to interfere to 14 any material extent with prompt movement of the power piston to any selected position in response to a change in pressure on either pilot diaphragm 3I or 32.

Summary From the above description it will now be seen that the improved hydraulic stabilizer is effective to insure stopping of a power member, such as the power piston 4, in a definite selected position without damaging shock. The structure of the stabilizer is such as to allow relatively free movement of the power piston substantially from one position to another or selected position in which it is desired that it shall stop. As the power piston substantially attains the selected position the stabilizer acts to provide a force for opposing further movement of said piston and said force so reduces the rate of piston movement as to insure the destruction of the actuating differential in fluid pressures on the piston when it obtains the position in which it is desired to stop same, so that further movement of the piston will be effectively prevented. In case of leakage of fluid under pressure from either power piston chamber, the resulting oscillatory movement of the piston does not open the valve controlled liquid flow communication in the stabilizer, so that the stabilizer remains effective to oppose and prevent any material change in the selected position of the power piston. The structure is so designed as to insure against the entrance of air into the pressure chambers which might materially interfere with or even destroy its stabilizing action.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In combination, a fluid motor comprising piston means subject to opposing fluid pressure in two chambers and being movable upon establishing a difierential between said pressures, regulating valve means for controlling the pressure of fluid in said chambers, control means operable to effect operation of said regulating valve means to establish said differential in fluid pressures, said piston means being operable upon movement relative to said control means to effect operation of said regulating valve means to destroy said differential in fluid pressures, stabilizer means comprising movable abutment means opposingly subject to liquid in two liquid filled control chambers, a constantly open restricted communication connecting said control chambers, means connecting said abutment means to move with said piston means, valve means operable to open and close a liquid flow communication between said control chambers, and actuating means for controlling said valve means operable to actuate said valve means to open said liquid flow communication upon operation of said regulating valve means to establish said differential in fluid pressures on said piston means and operable to actuate said valve means to close said liquid flow communication upon operation of said regulating valve means to destroy said differential.

2. In combination, a fluid motor comprising piston means subject to opposing fluid pressures in two chambers and being movable upon establishing a differential between said pressures, regulating valve means for controlling the pressure of fluid in said chambers, movable abutment means opposingly subject to liquid in two liquid filled control chambers, means operable upon movement of said piston means to actuate said abutment meansto displace liquid'from one of said control chambers to the other, a constantly open restricted communication connecting said control chambers, control valve means controlling a liquid flow communication between said control chambers, pilot means operable to operate said regulating valve means and said control valve means in unison to provide, respectively, a differential in fluid pressures on said piston means and to open said'liquid flow communication, and means operable by said piston means upon movement relative to said pilot means to effect operation of said regulating valve means to destroy-said difierential in fluid pressures on said power'piston and to at substantially the same time effect operation of said control valve means to close said liquid flow com,- munication.

3. In combination, a fluid motor comprising piston means subject to opposing fluid pressures in two chambers and being movable upon establishing a diiferen'tial between said pressures, regulating valve means for controlling the pressure of fluid in said chambers, movable abutment means opposingly subject to liquid in two liquid filled control chambers, means operable upon movement or said piston means to actuate said abutment means to displace liquid from one of said control chambers to the other, a constantly open restricted communication connecting said control chambers, control valve means controlling a liquid flow communication between said control chambers, pilot means operable tooperate said regulating valve means and said control valve means to provide respectively a difierential in fluid pressures on said piston 1 6 mearis'and to'open said liquidflow communication, means operable by said piston means upon movement relative to said pilot means to efiect operation-of said regulating valve means to destroy the differential in fluid pressures on said power piston and to at substantially the same time effect operation of said control valve means to close said liquid flow communication, a liquid reservoir disposed above said control chambers, said control valve means being also operable upon opening said liquid flow communication, to open to said reservoir the one of said control chambers receiving liquid from the other control control chamber, whereby liquid may also flow from said reservoir to the said one control chamber.

ARTHUR G. LARSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 250,103 Reynolds Nov, 29, 1881 259,538 Henszey June 13, 1882 333,831 Corliss Jan. 5, 1886 396,108 Nickerson Jan. 15, 1889 505,764 Harden Sept. 26, 1893 528,275 Martin Oct. 30, 1894 756,831 Clarke Apr. 12, 1904 887,517 Raub May 12, 1908 FOREIGN PATENTS Number Country Date 8,274 Great Britain 1915 

